Technical Support Report of Surge Bin Tower - Mine Safety and ...

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OWNERSHIP AND LOCATION REPORT NO. MWII-00S The Big Bend Quarry, Mine 1.0. No. 15-18147, is operated by Hilltop Basic Resources. The facil ity is located in Meade County, Kentucky, approximately 30 mi les southwest of Louisville, Kentucky. More precisely, the site has geographical coordinates 0[38°09'09" north latitude and 86°17'43" west longitude. INTRODUCTION The Big Bend Quany produces limestone from an open pit minc. The limestone is excavated by blasting and is run through a primary crusher in the pit before being transferred to the plant on the Overland Conveyor. The Overland Conveyor discharges into the 500-ton Surge Bin (photo 1) in the plant area before additional crushing and sorting is pClformed. The material stored in the Surge Bin is mostly 4 to 6 inches in diameter, The Big Bend Quan·y employs 35 miners and operates two shifts per day, 7 days a week. On Wednesday. November 10, 2010, at approximately 1:30 P.M., the 500-ton Surge Bin Tower coll apsed. No injuries were sustained because no one was on or near the tower at the time of the collapse. An cye witness account of the collapse noted a sudden drop of the Overland Conveyor' s head pulley, which was mounted on the top of the bin, followed by toppling of the bin toward the Overland Conveyor (west direction) (photo 2). The bin was at least one-half to three-quarters full and no material was being discharged into or out of the bin at the time of the collapse. On the day of the collapse, the wind speeds were low (10 MPH or less). Blasting in the pit (approximately II2-mile away) occurred 20 minutes before the bin collapsed. A seismograph located approximately II2-mile from the pit on residential property recorded a peak particle velocity below 0.0550 inches per second, which makes it is unlikely that the Surge Bin Tower vibrated at a frequency which would have damaged the structure. The level of the limestone in the bin is usually monitored by cameras and a tilt switch. The tilt switch had malfunctioned a few days before the collapse. The camera provides only a live feed to the plant operator booth, it does not record. The collapse of the Surge Bin Tower removed the end support from the truss supporting the Overland Conveyor. As a result. a 70-foot section of truss became partially detached, and was left hanging from the adjacent vertical bent support. The mine operator then proceeded to cut the belt and truss chords in order to bring the hanging section of the truss to the ground. The collapse of the Surge Bin Tower also damaged the tail of the Transfer Conveyor which was fed from the bottom of the bin on the east side. When the tail of the Transfer Conveyor was impacted, it caused the entire length of the Transfer Conveyor truss to thrust in the east direction, pennanently deflecting all of the bent supports to the east. The operator removed the truss and conveyor components of the Transfer Conveyor while we were on site and intends on repairing/replacing the bents of the Transfer Conveyor.
FIELD INVESTIGATION 2 On November 15 through 18,2010, Michael Superfesky and Anthony Argirakis worked with Sonia Conway, Metal and Norunetal Safety and Health Inspector, Lexington Field Office, by providing assistance regarding the safe removal of the damaged conveyor and bin stlUcture. An additional40·foot of new conveyor truss was installed at the end oflhe Overland Conveyor so that a stable cantilever was established until a new bin structure could be installed. Following the completion of this remedial work, the investigation of the Surge Bin Tower collapse commenced. The removal and installation of the new conveyor structure provided safe access to the area with little disturbance to the accident scene. A steady rain on November 16,2010, did produce a light coating of rust on the new fracture surfaces of the steel. MSHA was assisted during the investigation in collecting information and accessing the accident scene by the following Hilltop Basic Resources employees. John Morgan, Gary Lewis, Richard Popham, Kelly Carver, Configuration and Operation Vice President Mining Operations General Manager Quarry Manager Team Leader The Surge Bin Tower was configured with an overall height of 54 feet and square base 0[20.5 feet per side. Photo 1 shows the Surge Bin Tower approximately 5 years prior to the collapse. The main structural members of the tower consisted of four columns with lateral bracing between the columns, a 2-level orthogonal arrangement offIoor girders hung from the bin walls at the bottom, and stiffened bin walls which acted like plate girders (deep beams). The bin was square with interior dimensions of 20 feet by 20 feet and a height of28 feet. The bin was constructed by vertically stacking three prefabricated boxed sections (20 feet by 20 feet) together and bolting the box sections at each interface. The 3/4-inch-diameter bolts used for connecting tIle box sections were installed through the flange plates located on the top and bottom of each box section. The walls of each box section (bin walls) consisted of 1/4-ineh-thick steel plate stiffened on 2 foot centers using (non-bearing) steel angle sections with dimensions of 5 inches by 3 inches by 114 ineh. At the corners, the walls of the bin framed together at 90 degrees and were connected using a 1/4-inch fillet weld placed on the inside. The comers of the bin were stiffened for bearing purposes by welding two vertical steel bars (plates) 6 inches by 114 inch at 90 degrees to each other on the outside corners for the full 28-foot height of the bin. With respect to viewing the top of the bin from overhead, each corner of the bin, with the steel bar stiffeners attached, formed a cross. The attachment of the steel bar stiffeners to the bin corners helped in transferring the overall bin load (in bearing) to the columns below. The top of the columns had 3/4-inch-thick filler plates welded between both flanges on each side of the column's web to provide a bearing surface to connect the bottom of the bin corners and the bar stiffeners to the column. The bottom of the bin corners framed on top of the columns such that they interiorly rested upon one quarter of the total area provided by the filler plates and the column's web and flanges. Framing the bottom of the bin corner within an interior quadrant of the column top allowed the steel bar stiffeners to be welded to the top of the column. The weld
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Page 5 and 6: 4 material on the three other sides
Page 7 and 8: Failure Discussion 6 The collapse o
Page 9: Photo I - East side of Surge Bin To
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Technical Support Report of Surge Bin Tower - Mine Safety and ...

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